Comparative Braincase Morphology of Trilophosaurus buettneri and the Early Evolution of the Pan-Archosaurian Neurocranium
Comparative Braincase Morphology of Trilophosaurus buettneri and the Early Evolution of the Pan-Archosaurian Neurocranium
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DOI：
10.1080/02724634.2022.2123712
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发表时间：
2022-06
影响因子：
1.4
通讯作者：
Jacob D. Wilson;Anna L. Wisniewski;S. Nesbitt;G. S. Bever
中科院分区：
文献类型：
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作者：
Jacob D. Wilson;Anna L. Wisniewski;S. Nesbitt;G. S. Bever
来自最早的茎系历史的保存完好的化石相对稀缺，往往限制了我们建立健全的、基础广泛的进化模式的能力。这当然适用于始祖龙的泛辐射，相对于朝上的始祖龙，始祖龙最早的茎类仍然知之甚少。buettnertrilophosaurus buettneri是一种北美三叠纪的干始祖龙，位于这片广阔的泛辐射的底部附近。本文利用CT对三叉龙脑壳进行了研究，目的是阐明早期泛祖龙的神经颅骨及其演化。结果明确了几个有问题的特征，包括枕外融合不稳定、对侧枕外接触缺失、半月凹陷缺失等。这些新颖的评分不能改变大多数目前接受的树拓扑结构，但结果是详细的。这些数据还包括泛祖龙中最早的神经颅气化的系统发育证据，包括与冠祖龙的中咽隐窝位置同源的副蝶骨腔。这些数据并非没有问题，但它们确实让我们可以假设，在冠状祖龙更广泛的性格系统中，最早的转变是什么。多重自异形表明三叉龙有派生的行为技能，但细节尚不清楚。例如，三叉龙的前半规管有兽脚亚目的延伸，但缺乏相应的外侧管的扩张，这被认为有助于三叉龙的两足行走。我们的数据阐明了后来的祖龙转变的半胚性条件，同时支持了泛祖龙在其历史早期就实现了明显的结构和行为差异的假设。
ABSTRACT The relative scarcity of well-preserved fossils from the earliest history of stem lineages often limits our ability to establish robust, broad-based evolutionary patterns. This is certainly the case for the pan-radiation of archosaurs whose earliest stem taxa remain poorly understood relative to the crownward archosauriforms. Trilophosaurus buettneri is a North American Triassic stem archosaur that lies near the base of this expansive pan-radiation. We used CT to study the Trilophosaurus braincase with the goal of elucidating the early pan-archosaur neurocranium and its evolution. Results clarify several problematic characters including variable fusion of the exoccipital, absence of contralateral exoccipital contact, lack of a semilunar depression, and several others. These novel scorings fail to alter most currently accepted tree topologies, but the results are detailed. These data also include the phylogenetically earliest evidence of neurocranial pneumatization among pan-archosaurs, including a parabasisphenoid cavity that is positionally homologous to the median pharyngeal recess of crown archosaurs. These data are not without their problems, but they do allow us to hypothesize the earliest transformations in what became a much more extensive character system in crown archosaurs. Multiple autapomorphies suggest Trilophosaurus was capable of a derived behavioral repertoire, but details remain unclear. For example, Trilophosaurus bears a theropod-like elongation of the anterior semicircular canal but lacks the associated expansion of the lateral canal thought to facilitate bipedality in that group. Our data clarify plesiomorphic conditions for later archosaurian transformations while promoting the hypothesis that pan-archosaurs achieved marked structural and behavioral disparity early in their history.